A thunderegg (or thunder egg) is a

nodule Nodule may refer to: * Nodule (geology), a small rock or mineral cluster * Manganese nodule, a metallic concretion found on the seafloor *Nodule (medicine), a small aggregation of cells *Root nodule Root nodules are found on the roots of plants, ...

-like

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wale ...

, similar to a filled

geode A geode (; ) is a geology, geological secondary formation within sedimentary rock, sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter (which may include crystals) are secluded. The crys ...

, that is formed within

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...

volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...

layers. Thundereggs are rough

sphere A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

s, most about the size of a

baseball Baseball is a bat-and-ball games, bat-and-ball sport played between two team sport, teams of nine players each, taking turns batting (baseball), batting and Fielding (baseball), fielding. The game occurs over the course of several Pitch ...

—though they can range from a little more than a centimeter (one half inch) to over a meter (three feet) across. They usually contain centres of

chalcedony Chalcedony ( or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic ...

which may have been fractured followed by deposition of

agate Agate ( ) is a banded variety of chalcedony. Agate stones are characterized by alternating bands of different colored chalcedony and sometimes include macroscopic quartz. They are common in nature and can be found globally in a large number of d ...

jasper Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to ...

opal Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...

, either uniquely or in combination. Also frequently encountered are

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

crystals, as well as various other mineral growths and inclusions. Thundereggs usually look like ordinary rocks on the outside, but slicing them in half and polishing them may reveal intricate patterns and colours. A characteristic feature of thundereggs is that (like other agates) the individual

bed A bed is a piece of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many beds ...

s they come from can vary in appearance, though they can maintain a certain specific identity within them. Thunderegg is not synonymous with either geode or agate. A geode is a simple term for a rock with a hollow in it, often with crystal formation/growth. A thunderegg on the other hand is a specific

geological structure Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover informatio ...

. A thunderegg may be referred to as a geode if it has a hollow in it, but not all geodes are thundereggs because there are many different ways for a hollow to form. Similarly, a thunderegg is just one of the forms that agate can assume.

Occurrence

Thundereggs are found globally where conditions are optimal. In the US,

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

is one of the most famous thunderegg locations.

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

is also an important center for thunderegg agates (especially sites like St Egidien and Gehlberg). Other places known for thundereggs include

Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country located in the Horn of Africa region of East Africa. It shares borders with Eritrea to the north, Djibouti to the northeast, Somalia to the east, Ken ...

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...

Romania Romania is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to ...

Turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

, Mount Hay and

Tamborine Mountain Tamborine Mountain, also known simply as Mount Tamborine, is a plateau, geographic subregion and locality in the Scenic Rim Region of Queensland, Australia. In the , Tamborine Mountain had a population of 8,105 people. Geography The plate ...

(Australia), and the

Esterel massif The Massif de l'Esterel (Occitan Provençal: ''Esterèu''; English: Esterel Massif) is a Mediterranean coastal mountain range in the departments of Var and Alpes-Maritimes on the French Riviera. Neighbouring cities are Mandelieu-la-Napoule and C ...

(France).

Formation

Thundereggs are found in flows of rhyolite lava. They form in the lava from the action of water percolating through the porous rock carrying

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

in solution. The deposits lined and filled the cavity, first with a darker matrix material, then an inner core of agate or chalcedony. The various colors come from differences in the

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

s found in the

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

and rock that the water has moved through.

State rock designation

After an initiative by the Springfield Thunderegg Rock Club, on March 29, 1965, the thunderegg was designated as the Oregon

state rock Leaders of states in the U.S. which have significant mineral deposits often create a state mineral, rock, stone or gemstone to promote interest in their natural resources, history, tourism, etc. Not every state has an official state mineral, rock, ...

by a joint resolution of the

Oregon Legislative Assembly The Oregon Legislative Assembly is the State legislature (United States), state legislature for the U.S. state of Oregon. The Legislative Assembly is bicameral, consisting of an upper house, upper and lower chamber: the Oregon State Senate, Sena ...

.Chapter 186 — State Emblems; State Boundary
2017

Oregon Revised Statutes The Oregon Revised Statutes (ORS) is the Codification (law), codified body of statutory law governing the U.S. state of Oregon, as enacted by the Oregon Legislative Assembly, and occasionally by citizen Popular initiative, initiative. The statutes ...

While thundereggs can be collected all over Oregon, the largest deposits are found in

Crook Crook is slang for criminal. Crook or Crooks may also refer to: Places Canada * Crooks Inlet, former name of Kangiqturjuaq, Nunavut England * Crook, County Durham, a town * Crook, Cumbria, a village and civil parish * Crook Hill, Derby ...

Jefferson Jefferson may refer to: Names * Jefferson (surname) * Jefferson (given name) People * Thomas Jefferson (1743–1826), third president of the United States * Jefferson (footballer) * Jefferson (singer) or Geoff Turton (born 1944), British s ...

, Malheur, Wasco and Wheeler counties. The world's largest thunderegg, a 1.75 ton specimen, is housed by the

Rice Northwest Museum of Rocks and Minerals The Rice Northwest Museum of Rocks and Minerals is a non-profit museum in Hillsboro, Oregon, United States. Located just north of the Sunset Highway (Oregon), Sunset Highway on the northern edge of Hillsboro, the earth science museum is in the Po ...

Hillsboro, Oregon Hillsboro ( ) is a city in the U.S. state of Oregon and is the county seat of Washington County, Oregon, Washington County. Situated in the Tualatin Valley on the west side of the Portland metropolitan area, the city hosts many High tech, high-te ...

Legend

Native American legend reportedly considers the rocks to be the eggs of the thunderbirds which occupied

Mount Hood Mount Hood, also known as Wy'east, is an active stratovolcano in the Cascade Range and is a member of the Cascade Volcanic Arc. It was formed by a subduction zone on the West Coast of the United States, Pacific Coast and rests in the Pacific N ...

and Mount Jefferson. Thunder Spirits on the mountains hurled the "eggs" at each other.

Images

File:ThundereggOR.jpg, A thunderegg from Succor Creek on display at the

Oregon State Capitol The Oregon State Capitol is the building housing the Oregon Legislative Assembly, state legislature and the offices of the Governor of Oregon, governor, Oregon Secretary of State, secretary of state, and Oregon State Treasurer, treasurer of t ...

File:Agat stratyfikowany, thunderegg- Falen Tree, Oregon, USA..jpg, A thunderegg agate from Falen Tree, Oregon, US File:Thunderegg.jpg, A jasper thunderegg from White Fir Springs, Oregon File:Friend ranch-thunderegg.JPG, A Friend Ranch thunderegg from Oregon File:Gehlberg Geode.JPG, A thunderegg geode from

Gehlberg Gehlberg () is a village and a former municipality in Thuringia, Germany. Formerly in the district Ilm-Kreis, it is part of the town Suhl Suhl () is a city in Thuringia, Germany, located SW of Erfurt, NE of Würzburg and N of Nuremberg. W ...

, Germany File:Esterel-agate.jpg, A thunderegg agate from the south of France File:Agat Thunderegg x 2 - Richardson Ranch (Priday Ranch), Madras, Jefferson Co.jpg, Two double thundereggs from Richardson Ranch (was known as Priday Ranch), Madras, Oregon File:Opal filled thunderegg - Rice NW Museum.JPG, Largest opal-filled thunderegg in the world, from Opal Butte in Oregon

References

{{Reflist

External links

''Geode Kid's Collection in Deming New Mexico'' on Mindat

Geologic Snowflake Hunters Flock To Oregon For Thundereggs
Documentary produced by

Oregon Field Guide ''Oregon Field Guide'' is a weekly television program produced by Oregon Public Broadcasting focusing on recreation, the outdoors, and environmental issues in the state of Oregon. The show has become part of the Oregon zeitgeist. Steve Amen is th ...

Gemstones Minerals Igneous rocks Symbols of Oregon Cascadian folklore